As already known, the performance of a cyclist depends on several factors:
1—the power developed both by the torque during pedalling and by the cyclist capacity to create a high rotary motion using an average transmission ratio;
2—the aerodynamic position of the cyclist which reduces the frictional forces and allows a better penetration in the air; and
3—the different mechanical elements composing the bicycle: they must be of good quality to facilitate their movement and the braking.
On the mountains weight plays an important role due to the action of gravity on the assembly consisting of the bicycle and the cyclist. Comfort is appreciated, especially over long distances, as it makes more bearable the physical effort. A good rigidity provided by the structure allows an energy transfer from the cyclist to the wheels of the bicycle with a good yield. However, it is commonly known that an excessive rigidity negatively influences the physical abilities of the cyclist.
Therefore, the cyclist's performance is due to a skilful blend of all of the above factors.
In addition, weight and support distribution condition the holding of the wheel and its stability.
The yield of a modern bicycle is very high, in the sense that 97% of the power generated by the cyclist is used for the thrust of the velocipede. However, probably currently available bicycles do not allow the cyclist to use all the energy he has for thrusting the bicycle.
For example, taking into account the transmission of movement through a chain to the rear wheel by means of the rotation of the crank disc, a rotation produced by the alternated movement of the legs of the cyclist, the problem is not to increase the transmission efficiency, which, as previously said, is already about 97%, but to prevent this performance from drastically diminishing due to changes in the route conditions.
Two lines of research seem currently possible:
1—Designing a pedal which makes the most of the energy developed during the cyclist pedalling. This, for example, is the goal of the oval pedal. That pedal is designed to facilitate the passage through two dead points met while pedalling. That depends on the angle between the cranks in relation to different orientations of the gear.
2—Avoiding a too low inertia of the wheel during rotation, so that the efficiency does not drop too. Indeed, a lightweight wheel has a low initial inertia of rotation and can immediately provide an ease of feeling in pedalling with considerable starting acceleration. However, the initial positive effects deriving from the equipment of lightweight wheels can quickly backfire against the cyclist, who must prolong his/her physical effort to maintain the at first easily reached speed. In other words, a lightweight wheel does not store enough kinetic energy for giving it back (potential energy) thereafter, and if the cyclist is not perfectly fit, it can cause considerable negative consequences.
The invention is precisely based on this second line of research.
Accordingly, the present invention is based on the observation that, although it is true that an excessive overall weight of the bicycle/cyclist system is generally a negative factor, especially uphill, there is also some weight which, if adequately distributed on the bicycle, and in particular on the rim, can significantly improve the pedalling yields in particular conditions.
The present invention is essentially based on the use of centrifugal masses attached to the rims of the bicycle. From a static point of view, these centrifugal masses can lead to an increase in the weight of the bicycle comprised between 60 and 80 grams per wheel.
If these centrifugal masses, which are profiled wing-shaped projections, are fixed on lightweight wheels with low inertia, from a dynamic point of view these masses (due to developing centrifugal forces) apply a force on the rim shaft (from the inside to the outside). Such masses contribute, therefore, to reduce the tension loss due to different lateral forces applied to the hubs.
At low speeds, the mobility of the hub is significantly increased by maintaining an effective increasing radius (decrease of the vertical deflection by means of a stiffness increase). The uneven mountain roads are no longer a problem, and the comfort of the bicycle considerably increases. The bicycle reacts well to quick starts, and when the speed increases the wheel stiffens, thus allowing a better road handling downhill.
The shape of the dynamic masses and their weight are factors that contribute to improve the hold of the wheel on the axis of symmetry, and, consequently, the quality of performance provided by the pedal is optimal and the lateral deformation is reduced.
The passages through the (upper and lower) dead points are easily performed and the cyclist uses less energy to keep pedalling.
Moreover, as already known, the use during competitions (e.g. for timed competitions (called “races against the clock”)) of solid wheels having an ultra-rigid composite structure has increased the overall performance of the bicycle. In spite of that, the side wind sensitivity of the wheels is a major handicap, and if weather conditions are not good, their use could prove dangerous.
For such a kind of races, it would be possible to continue to use traditional wheels with spokes, much less susceptible to wind, with lower but heavier centrifugal masses, conferring the required rigidity to the wheel.
It would be possible to vary, in a modular way, the shape of the centrifugal masses and their weight according to the type of racing, on the mountains, on the plains, or timed (called “races against the clock”).
The materials used may be composite carbon/Kevlar™, or other fibres which have shown to get a good tensile strength.
Some plastics, such as, for example, ABS (acrylonitrile butadiene styrene), allow to reduce costs and to facilitate the diffusion of such devices.
For those applications, specifically designed rims are necessary because the present invention also concerns an anchoring system of the centrifugal masses.
The slide rail for the centrifugal masses can be formed in the thickness of the rim (negative rail), or a rail system can be adopted (positive rail).
In all cases, the centrifugal masses are not bonded to the rim but slidable with respect to the rim. This is important because it allows the system to adequately distribute the pressures exerted on the inner surface of the rim.